Regulation system for the short circulation and headbox of a paper machine or equivalent

ABSTRACT

A headbox ( 10 ) has a stock inlet header, a tube bank, a tubulence generator and a slice channel. Measurement targets (P A , P B , P C , P, P E ) are provided with means for making measurements of the fiber mobility of the fiber suspension, then controlling the flow state of the suspension. Sensors on the width of the headbox ( 10 ) or traversing sensors are positioned on different width points of the headbox ( 10 ) and arranged to measure the fiber mobility profile, with means for changing the flow state on the basis of the measurements. Apparatus for diluting the thick stock into headbox consistency and units for cleaning the stock to be fed into the headbox may be provided. Sensors may be disposed in the short circulation pipes or cleaning units arranged to measure the fiber mobility of the fiber suspension with means for changing the flow state on the basis of the measurement data.

BACKGROUND OF THE INVENTION

The present invention relates to a method in the measurement and controlof the short circulation and the headbox of a paper machine orequivalent. The present invention relates also to a headbox and theshort circulation.

The invention relates to the arrangement of the short circulation andthe headbox of a paper machine or equivalent. The paper machine orequivalent refers in the present context to a machine with whichpaper-like product such as paper, board or tissue paper is produced.

The stock feeding of the paper machine is in general as follows. Thestock components are stored in the paper mill in separate storage tanks,wherefrom they are fed into proportioning tanks and therefrom furtherinto a common mixing tank, in which the stock components are intermixed.From the mixing tank the stock is fed into a machine tank, wherefrom thestock, being in general in about 3% consistency, is fed into ashort-circulation wire pit. In the wire pit the thick stock is dilutedinto a headbox consistency, which is in general about 1%.

The fibres and fillers to be used as raw material are taken to the wirethrough a headbox and conveyed by water. The filtrate having passedthrough the wire, containing fibrous agents and fillers in greatquantities, is returned as a filtrate of the thick stock from themachine tank back to the wire through the headbox. A flow link thusformed is called a short circulation.

Impurities may enter in the short circulation together with the thickstock or through other ways which have to be removed before the headbox.This is carried out with short-circulation cleaning apparatus, such ashydrocyclones, screens, machine screens and deaeration tanks.

The short circulation together with the headbox in connection therewithis in general considered as the most sensitive part of the papermakingprocess. Any small changes in the consistency, flow or other parametersimmediately affect the quality of the paper being manufactured or causeweb breaks on the paper machine. The function of the short circulationin the papermaking is, among other things, to produce a fibre suspensionof uniform quality, in which the various components (fibre fractions,chemicals and fillers) are intermixed into a homogeneous fluid. The goodhomogeneity of the stock thus produced will guarantee a uniform qualityin the paper and an undisturbed production process in subsequent phases.

In the papermaking, one of the important functions of the headbox isformation of slice jet to be optimal in its flow state. In an optimalslice jet, the solid matter is distributed homogeneously, the floc sizeis optimal, the disturbances are minimal, and the turbulence level isunder control. The essential measurable and controllable quantity is thedegree of suspension fluidization, illustrating the intermobility offibres. In the headbox, various geometrical designs are used forfluidizing the suspension, such as step changes of flow channels,adjustments of trailing elements and various surface phenomena, such asboundary layer turbulence, wherewith turbulence is generated in the flowof the suspension.

In the prior-art OptiFeed process of Metso Paper, Inc., described inpatent specification FI-103676, the stock entering the paper machine isbuilt from a number of separate (2-4) stock components, the fibrousproperties of which deviate from each other and vary along with changesof the paper grade to be manufactured. The stock components are mixedinto homogeneous fluid in so-called mixing reactors located in the partsof the short circulation to which several stock components are broughtsimultaneously.

The operation of the OptiFeed process is dependent on the goodness ofthe operation of the mixing reactor. In an optimal situation, the mixingshould be as perfect as possible and in addition, to work for all papergrades being manufactured, even though the flow quantities of differentcomponents, depending on the quality, may vary to a great extent. Thegoodness of the mixing of different components being mixed as known inthe art can be measured and controlled when an optimal operation is tobe secured. The mixability of suspensions containing fibrous matter isdependent on the mobility of solid matter and the turbulence generatedtherethrough. Optimizing the generation of turbulence is implementablee.g. by means of various adjustable throttling elements, disclosed e.g.in the patent application of Metso Paper, Inc. No. FI-992015.

In the flow of fibre suspension, the fibres tend to form accumulationscalled flocs. If the consistency of the flow exceeds the sedimentationconsistency, the flocs are built into a net-like united phase, which inthe papermaking is an undesired state. The state in which the structureis completely decomposed is called fluidized. In mixing a fibroussuspension, momentary fluidization of components to be mixed isexpected. The mixing is in general carried out by conducting flows ofdifferent components into one at different speeds. If the state offluidization can be monitored, the differential speed required (shearingstress between the flows being mixed) can be set optimal. In connectionwith the fluidization, the structure of a fibre net or flocs isdecomposed. Hereby, the state of fluidization can be estimated with theaid of floc size and its completeness with the aid of the minimum sizeachieved. The floc size measuring in the process circumstances is verydifficult in practice.

Generating turbulence in the fibre suspension causes breaking up offibre flocs and increased intermobility of individual fibres. Providingfluidization by increasing the turbulence requires geometric changes toadd shearing stresses or a surface of a flow channel or a trailingelement to produce sufficient boundary-layer turbulence. Increasedfluidization as such will not cause reduction of turbulence. The fibresuspension usually tends to become re-flocculated so to speak, which canbe observed as reduced fibre mobility (degree of fluidization). On theother hand, the properties of turbulence include so-called dissipation,which means changing of the kinetic energy of the turbulence intointernal energy (heat) of the fluid. However, the degree of fluidizationof the suspension will be decreased owing to the dissipation ofturbulence. Thus, the fluidization of the suspension is a transientstate, the follow-up of which is essential for the success of thepapermaking process.

SUMMARY OF THE INVENTION

The objective of the present invention is to develop a method and anapparatus for real-time measuring of the short circulation of a papermachine or equivalent and of the fibre mobility of the suspension of theheadbox and for controlling the flow state.

The objective of the present invention is also to provide a method andan apparatus, wherewith as optimal mixability of the fibre suspension aspossible is guaranteed in different parts of the short circulation andthe headbox so that the fibre suspension is in an optimal state for thesubsequent phase of the process.

The method according to the invention is mainly characterized in that inthe method, the selected measurement targets are provided with means formeasuring the fibre mobility of the fibre suspension, and on the basisof the fibre mobility measured from the fibre suspension, the flow stateof the fibre suspension is controlled.

The headbox of the invention is in turn characterized in that theheadbox comprises sensors on the width of the headbox or a traversingsensor/sensors, being fitted in different width points of the headbox,and that a sensor/sensors is/are arranged to measure the fibre mobilityprofile of the headbox on the width of the entire headbox and that theheadbox comprises means for changing the flow state on the basis of themeasurement data obtained from the sensors.

The short circulation of the invention is characterized in that theshort circulation comprises a sensor/sensors, disposed in the pipes ofthe short circulation and/or in the cleaning apparatus, and that asensor/sensors are arranged to measure the fibre mobility of the fibresuspension in the short circulation and that the short circulationcomprises means for changing the flow state on the basis of themeasurement data rendered by the sensors.

According to the invention, the apparatus components used forcontrolling the mixture in the short circulation of a paper machine orequivalent are provided with sensors measuring the flow state, on thebasis of the data obtained wherefrom the flow state is controlled bymeans of control devices. With a measurement and control system such asthis, the furnish of the fibre suspension is controlled to be such thatit is optimal for the next process phase. The solution according to theinvention can be used also in cardboard and tissue machines.

In addition, with the method according to the invention, the fibremobility of the suspension of the headbox can be measured most preciselyon the entire width of the slice channel. The slice channel is providedwith a row of sensors, a sensor matrix or a traversing sensor, in whichthe degree of fluidization of the suspension is measured in real time.In multiple-layer headboxes, a row of sensors or a sensor matrix ispositioned on each layer. On the basis of the measurement data obtainedfrom the sensors, the flow state of the suspension of the headbox iscontrolled, in order to make the fibre mobility, that is, the degree offluidization, optimal. When the optimal range of variation of the fibremobility is known for different paper grades, the quality of the paperproduced can be controlled in changing running circumstances. Theoptimal range of variation of the fibre mobility can be determinedexperimentally.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described more in detail with reference to theaccompanying figures, in which

FIG. 1 is a principle block diagram representation about measurement andcontrol of solid matter mobility in the short circulation.

FIG. 2 presents development of fibre mobility as a function of residencetime t.

FIG. 3 presents a short circulation process arrangement.

FIG. 4A presents an example of the structure of a short circulationmixing reactor.

FIG. 4B presents an actuator for controlling the mixing in a shortcirculation mixing reactor with the actuator in open position.

FIG. 4C presents the actuator of FIG. 3B in partly closed position.

FIG. 5 presents an example of positioning a sensor matrix of theinvention in the slice area of the headbox and the control system of theinvention.

FIGS. 6A, 6B and 6C present one embodiment of a turbulence adjustersleeve to be disposed in a flow channel.

FIGS. 7A and 7B present a second embodiment of a turbulence adjustersleeve to be disposed in a flow channel.

FIG. 8 is a view taken at line 8—8 in FIG. 4B.

FIG. 9 is a view taken at 9—9 in FIG. 4C.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 presents a model for optimizing the mixing of fibre suspension.On principle level, FIG. 1 presents a mixing reactor MR equivalent tothe part of the short circulation to which one or more components C₁,C₂, C₃, C₄ are supplied to be mixed in the mixing reactor MR into asuniform mixture as possible. The fibre properties of the components C₁,C₂, C₃, C₄ to be mixed deviate in general from each other and theirmutual ratio varies according to the paper grade to be produced. Thecomponents C₁, C₂, C₃, C₄ to be mixed are mixed in a controllable mixingelement ME. According to the invention, in the volume after the mixingelement ME, a mixing sensor MS is positioned to measure the homogeneityof the mixture. From the output of the mixing reactor MR, a stock flowmix is obtained, which is controlled so that its furnish is optimal aspossible for the subsequent phase of the process. From the sensor MS, ameasuring signal S₁ is obtained which is taken to the mixing controlunit MC to send a control signal S₂ to a mixing element MR₁. In thismanner a feedback is formed with which the control of the furnish of theinvention can be carried out.

In the measurement and control system described above, the sensors to beused for measuring a flow state are e.g., rapid pressure sensorsmeasuring pressure variations or surface friction sensors measuringacceleration. Also with different optical methods, with e.g.laser-Doppler anemometer, fibre mobility can be measured, as well aswith sensors based on radioactive radiation, microwave measurement orultrasonic sensors. On the basis of the measured fibre mobility data,turbulence is brought into a flow state, wherewith the mobility of thefibre suspension is controlled to be optimal. The volume being measuredfrom the fibre suspension in a target being measured is tried to beselected so that it is the smallest element in which the fibres andother ingredients are mixed uniformly. The size of such volumetricelement is dependent, for instance, on the medium length of fibres andits ideal size varies in different parts of the process and is dependenton the product being produced.

When the fibre mobility is measured with methods described above,information is obtained on the mobility of individual fibres, which hasbeen found to describe well the level of floc size and fibre networkforming. Indirect data can be obtained from the fibre mobility about theintensity of the turbulent movement of fibres, about the parameters ofthe location correlation and the parameters concerning the shape of thevelocity distribution. The graph depicted in FIG. 2 describes theintensity I of the movement of fibres of the fibre suspension, that is,development of the fibre mobility as a function of the residence time t.The intensity I of the fibre movement is inversely proportional to thefloc volume. The graph is divided into four parts, in part 1 of whichthe fibre mobility of the fibre suspension is presented beforefluidization, whereby the floc size is great and the mobility of fibressmall. In part 2, the fibre suspension is fluidized, whereby the fibremobility increases and the floc size reduces. Thereafter,re-flocculation follows in part 3, whereby the fibre mobility reduces asa function of time, until the flow state ends into a saturation state inpart 4, in which the fibre mobility no longer significantly diminishes.

FIG. 3 presents a short-circulation process arrangement, in which suchprocess targets are presented in which the measurement and controlarrangement of the mixing presented in FIG. 1 can be applied.

As shown in FIG. 3, the headbox 10 in short circulation feeds throughits slice opening a stock suspension jet into the wire section 100. Fromthe wire section 100, the water collecting apparatus conduct the waterdischarged through the wire as a flow F₅₀ into the wire pit 50. To themixing area 50 a of the mixing pit 50, a fresh stock flow M_(T) is fed,the consistency whereof being in general on the order of 3%. While inthe wire pit 50, the fresh stock is diluted into headbox consistency onthe order of 1%. To the mixing area 50 a of the wire pit 50, the suctionside of a pump 51 is connected. From the pressure side of the pump 51, astock flow F₆₀ diluted into the headbox consistency is directed throughthe hydrocyclones 60 to a deaeration tank 70.

In the deaeration tank 70, the air volume prevailing in underpressure islocated above the free surface of the stock. The height of the stocksurface is determined by the overflow 70 a of the deaeration tank 70,across which a stock flow F₇₀, is flowing, from which the air isremoved. Said stock flow F₇₀ is conducted to the mixing area 50 a of thewire pit 50. In addition, a return flow F₆₁ is brought into said mixingarea 50 a from the accept of the second phase hydrocyclones. A freshstock flow M_(T) is also brought into said mixing area 50 a. From thelower part of the deaeration tank 70, a stock flow F₇₁ is conducted tothe suction side of the pump 71. The pump 71 feeds the inlet stock flowF_(in) through the machine screen 80 to the stock inlet header of theheadbox 10. The bypass F_(out) of the stock inlet header of the headbox10 is returned to the deaeration tank 70. Reject F₈₁ of the machinescreen 80 is conducted to treatment of rejects.

According to the invention, targets appropriate for measuring andcontrolling the flow state in short circulation are the positions markedin the figure; in position P_(A) in connection with the mixing area 50 aof thick stock and wire water, in position P_(B) in connection with thehydrocyclone unit 60, in position P_(C) in connection with thedeaeration unit 70, in position P_(D) in connection with the machinescreen 80.

FIG. 4A presents a mixing reactor MR, in which the control of the flowstate according to the invention is implemented in the shortcirculation. Into the mixing reactor MR, two or more components C₁, C₂,. . . , are brought to be mixed, which are tried to get mixed into ashomogeneous a stock mix F_(mix) as possible. Said mixable components arefor instance, thick stock and wire water.

FIG. 4B presents an actuator with which the control of the flow state ofthe invention can be implemented in mixing reactors MR located indifferent process phases of the short circulation, in which thecomponents C₁ are mixed in the outer pipe t₁ and the C₂ in the innerpipe t₂. Component C₁ is, e.g., thick stock and component C₂, wirewater. According to the invention, in the outlet end of the inner pipet₁ of the mixing reactor, so-called delta wings d_(i) are installed, theangle whereof being controllable with an exterior control. The outletend of pipe t₁ comprises six delta wings d_(i) in the present example,the angle of which is controlled by means of control actuators d_(C).There may be also some other number of delta wings d_(i) available. Byopening the delta wings d_(i), the outer flows can be restricted.

By closing the delta wings d_(i), the inner pipe can be closed partly orentirely, so that no harmful dead volume is left in the inner pipe. Theshape of the delta wing of the design of the invention is a highlyefficient turbulence generator. FIG. 4C presents a delta wing structureof the invention, in which the delta wings d_(i) limit more the flow ofthe inner pipe t₂.

In addition to what is described above, also other control means can beused for controlling the flow state in the short circulation. Such meansare for instance controllable pipe expansions positioned before thecleaning units (hydrocyclones, deaeration tanks), in which the diameterof the pipes and or the location of a pipe expansion can be adjusted,and controls to be implemented in the machine screen, in which the wingangle, distance of the wing, pressure and/or speed of rotation can becontrolled. In addition, controllable throttles can be positioned beforethe cleaning units.

FIG. 5 presents the headbox 10 of a paper or board machine, comprising astock inlet header J, tube bank 11, an intermediate chamber 12, aturbulence generator 13 and a slice channel 14. The headbox 10 isprovided with a row of sensors or sensor matrix S₁₁, . . . , S_(nm), inwhich the overall number of sensors is n x m. In the embodiment of FIG.4, the sensors S₁₁, . . . , S_(nm) are attached to the slice channel 14so that the sensors S extend on the width and length of the slicechannel 14. With the sensors S, the mobility of suspension fibres aremeasured and the sensors S are positioned preferably at equal distancese.g. 60 mm from each other. The sensors S can be positioned on the upperand lower surface of the slice channel in one-layer headboxes. Inmulti-layer headboxes the sensors S can be positioned on each layer.With one row of sensors, a momentary transverse profile illustrating themobility of fibres can be measured. Using a sensor matrix, informationcan be moreover received about the fibre mobility in machine direction.The sensors S₁₁, . . . , S_(nm) are attached to e.g. a slice cone, onthe surfaces of the trailing elements or the tube bank and measuringsignal leads are drawn therefrom to the receiving unit 20 processing themeasurement data and transmitting it to the control unit 30 of theheadbox. It is also possible to use a traversing sensor which keepsmoving in cross-machine direction.

The mode of operation of the fibre mobility sensors can be based on anumber of different quantities. The measurement can be performed e.g. onthe basis of rapid pressure variations, whereby pressure sensors areused, or on the basis of acceleration, whereby surface friction sensorsare used. Using various optical methods, e.g. laser Doppler anemometer,fibre mobility can be measured such as with sensors based on radioactiveradiation, microwave measurement or ultrasonic measurement. On the basisof the fibre mobility data measured, such turbulence is generated in theflow state, with which the mobility of the fibre suspension iscontrolled to be optimal.

The headbox control unit 30 controls the transverse control ofturbulence according to the invention in the headbox. For controllingthe turbulence, a plurality of different methods and apparatus are knownin the art. In U.S. Pat. No. 4,133,713, an arrangement is disclosed inwhich the turbulence is controlled by changing the length of thetrailing element. Turbulence can also be generated by means of variousgeometric designs, such as step changes of flow channels and by means offlow channel surface structure (e.g. surface roughness, materials).

FIGS. 6A-6C and 7A-7B present a turbulence adjuster sleeve T to bedisposed in the flow channel, wherewith the turbulence is adjusted withtwo nested sleeves T₁ and T₂ so that the inner sleeve T₂ is moved byrotating and/or pushing it relative to the outer sleeve T₁. The innersleeve T₂ has a geometrical form wherewith an abrupt change is producedin the flow state and thus, turbulence at said point. Adjuster sleeves Tcan be positioned e.g. in the channels 13 _(a11), 13 _(a12), . . . ofthe turbulence generator.

FIG. 6A presents in more detail a first way of adjusting the adjustersleeve T of the invention, in which the flow state is changed byrotating the inner sleeve T₂. FIGS. 6B and 6C present section C—C ofFIG. 6A, in which the inner sleeve T₂ is adjusted into two differentpositions for controlling the degree of turbulence.

FIG. 7 presents a second adjustment form of the adjuster sleeve T. Inthis embodiment, the sleeve disposed within the flow pipe is moved inthe machine direction, so that the adjustment is produced in thegeneration of the turbulence caused by the sleeve. In FIGS. 7A and 7B,by pushing the adjuster sleeve T disposed within the flow pipe V intodifferent directions, a change can be produced in the flow state.

The rotation of the sleeve relative to its axis and/or moving it in themachine direction generates controlled changes in the strength andorientation of turbulence. By said mechanisms, e.g. control ofturbulence intensity is obtained after the turbulence generator, that isat the beginning of the slice channel. Hence, it is also possible toprofile the turbulence and consequently, also the fluidization of thesuspension in cross-machine direction and/or in Z direction.

In the following, the patent claims will be given, and different detailsof the invention can show variation within the scope of the inventiveidea defined in said claims and differ from what has been stated aboveby way of example only.

What is claimed is:
 1. A method for measuring and controlling a shortcirculation in a headbox of a papermaking machine, said shortcirculation comprising apparatus for diluting stock into a headboxconsistency and apparatus for cleaning the stock to be fed into theheadbox, and wherein the headbox comprises a stock inlet header, a tubebank, at least one turbulence generator and a slice channel, the methodcomprising the steps of: measuring fibre mobility of stock at a selectedmeasurement target in the short circulation; on the basis of the fibremobility measured at the selected measurement target, adjusting aportion of the short circulation to control the stock mobility at leastat the selected measurement target.
 2. The method of claim 1, whereinthe mobility at the selected measurement target is controlled to produceflow optimal for a further part of the short circulation in a headbox ofa papermaking machine.
 3. The method of claim 1 wherein the step ofmeasuring the fibre mobility in the selected measurement target in theshort circulation is performed using a sensor selected from the groupconsisting of: pressure sensors, acceleration sensors, opticalphenomenon sensors, radioactive radiation sensors, ultrasonic sensors,and microwave sensors.
 4. The method of claim 1 wherein the selectedmeasurement target is selected to be a region no bigger than that inwhich fibres and other ingredients are mixed uniformly.
 5. The method ofclaim 4 wherein the step of continuously measuring within the headbox across machine direction mobility profile is accomplished with an arrayof mobility sensors which extend in the cross machine direction and aremounted to the headbox.
 6. The method of claim 4 wherein the step ofcontinuously measuring within the headbox a cross machine directionmobility profile is accomplished by moving at least one mobility sensorin the cross machine direction on the headbox.
 7. The method of claim 4wherein a plurality of turbulence generators are positioned within theheadbox and the plurality of turbulence generators is arranged to form across machine direction extending array.
 8. The method of claim 1,wherein the portion of the short circulation adjusted to control thestock mobility is a mixing reactor which is provided with delta wingswhich are adjustable and wherein the stock mobility is controlled byadjusting the angle of the delta wings.
 9. The method of claim 1 whereinthe selected measurement target in the short circulation is selectedfrom the group consisting of: a mixing area of wire water and a thickstock, a hydrocyclone unit, a deaeration unit, and a machine screen eachof which is positioned in the short circulation.
 10. The method of claim1 further comprising measuring fibre mobility in a plurality oflocations in a transverse direction in the headbox to determine atransverse fibre mobility profile for the headbox, and controlling themobility of the headbox based on the transverse fibre mobility profile.11. The method of claim 10 wherein the step of controlling the mobilityof the headbox includes the step of adjusting a flow structure withinthe headbox.
 12. The method of claim 1 further comprising the step ofpositioning a plurality of fibre mobility sensors fin the slice channel.13. The method of claim 1 wherein a sensor selected from the groupconsisting of pressure sensors, acceleration sensors, optical phenomenonsensors, radioactive radiation sensors, ultrasonic sensors, andmicrowave sensors, is moved in the cross machine direction.
 14. Themethod of claim 1 wherein in the mobility of the fibre suspension iscontrolled before the fibre mobility measurement.
 15. A method offorming a paper web on a papermaking machine comprising the steps of:flowing a quantity of papermaking stock through a headbox to form across machine direction extending stock suspension jet; feeding the jetinto a wire section of the papermaking machine; continuously measuringwithin the headbox a cross machine direction mobility profile; andresponsive to the cross machine direction mobility profile adjusting atleast one turbulence generator positioned within the headbox.
 16. Aheadbox of a paper machine, comprising: stock inlet header; a tube bankin stock receiving relation with the stock inlet header; a turbulencegenerator in stock receiving relation with the tube bank; a slicechannel in stock receiving relation with the turbulence generator; aplurality of means for measuring fibre mobility arrayed in the crossmachine direction and mounted to the headbox, and means for changingmobility of stock within the headbox on the basis of measurement dataobtained from the sensors.
 17. The headbox of claim 16, wherein thesensors are disposed in the slice channel of the headbox.
 18. Theheadbox of claim 16, wherein the sensors are arranged into a matrixdisposed in the slice channel of the headbox.
 19. The headbox of claim16, wherein the means for changing mobility of stock includes means forcontrolling the transverse turbulence profile of the headbox.
 20. Theheadbox of claim 16, wherein th means for controlling the transverseturbulence profile of the headbox includes individual turbulencegenerators which are provided with adjustable sleeves.
 21. A shortcirculation of a paper machine, comprising: a wire pit; apparatus fordiluting thick stock into headbox consistency stock; apparatus forcleaning stock to be fed into the headbox; a headbox; piping connectingthe wire pit to the apparatus for diluting thick stock into headboxconsistency stock, and connecting the apparatus for diluting thick stockinto headbox consistency stock to the apparatus for cleaning stock, andconnecting the apparatus for cleaning stock to the bead box; a sensorarranged within the short circulation of the paper machine to measurethe fibre mobility of the fibre suspension in the short circulation; ameans for changing the mobility at a selected location within the shortcirculation, the means in data receiving relation to the sensor, themeans forming a part of the short circulation of the papermaking machinedata receiving relation to the plurality of fibre mobility sensors. 22.The short circulation of claim 21, wherein the sensor is positioned inthe apparatus for diluting thick stock into headbox consistency stock.23. The short circulation of claim 21, wherein the sensor is positionedin the apparatus for cleaning stock to be sent to the headbox.
 24. Theshort circulation of claim 21, further comprising a hydrocyclone unitconnected by the piping between the apparatus for diluting thick stockinto headbox consistency stock and the apparatus for cleaning stock,wherein the sensor is positioned in the hydrocyclone unit.
 25. The shortcirculation of claim 24, further comprising a deaeration unit connectedby the piping between the apparatus hydrocyclone unit and the apparatusfor cleaning stock, wherein the sensor is positioned in the deaerationunit.
 26. The short circulation of claim 21, wherein the means forchanging the mobility is positioned before the sensor.
 27. A headbox ina papermaking machine comprising: a stock inlet header; a tube bank instock receiving relation with the stock inlet header; a slice forming aslice channel in stock receiving relation to the tube bank; a pluralityof fiber mobility sensors mounted on the slice, to form a cross machinedirection array which provides a cross machine direction mobilityprofile; a plurality of structures for producing adjustable turbulencepositioned in the headbox, in data receiving relation to the pluralityof fiber mobility sensors, the plurality of structures for producingturbulence being adjustable so as to control the cross machine directionmobility profile.